This invention relates to a scaling device for elevator cars and more particularly to such a scaling device that is so constructed as to stay free of any influences by deformation of a car floor.
Generally in elevators or lifts, in order to prevent overloading, there is provided a scaling device for weighing load of the weight of passengers applied on the car floor so that the car will not operate when it is oveloaded.
In conventional scaling devices for elevator cars, a load is detected by detecting the amount of deformation of rubber vibration insulators, which are mounted at each corner on the bottom of the car floor to reduce the vibration of the car floor. Load detecting beams, each end of which is rigidly jointed to the car floor, are provided at the underside of the car floor and arranged to subside in conformity to the deformation of the rubber insulators. A load detecting switch is mounted on a supporting frame on which the car floor is fixed through the rubber vibration insulators. In this arrangement, the rubber insulators deform by the load on the car floor and the load detecting beams subside in conformity to the deformation of the rubber insulators. When the load is in excess of the predetermined weight, the detecting beams turn on the load detecting switch thereby to stop the operation of the car. Under a nonloaded condition, the gap between the detecting beams and the detecting switch is adjusted such that it becomes equal to the amount of the deformation of the rubber insulators at a state in which the rated load is applied on the floor. Such a gap adjustment has been made after the installation of the car by loading a weight corresponding to the rated load.
However, as such a gap adjustment is practiced at a site of a car installation, it is necessary to carry out the work under the car floor in a narrow car passage, so that the workability of the gap adjustment is extremely bad and it is very difficult to provide consistent accuracy.
Another problem associated with the conventional scaling device for an elevator car arises from deformation of the car floor by the weight of the load on the floor. That is, when a load is applied, the car floor deforms in bow-shape and the rubber insulators do not subside uniformly but each is slanted at its upper surface where the car floor is fixed. As a result, the detecting beams rigidly jointed along with the rubber insulators on the car floor receive a bending moment at both ends thereof and flex in bow-shape. Therefore, in addition to the flexure caused by deformation of the rubber insulators, the detecting beams are further flexed at their middle portion owing to the bending moment. Therefore it is necessary to adjust the gap between the detecting beams and the detecting switch, considering not only deformation of the rubber insulators but also the flexure of the detecting beams by deformation of the car floor.
The amount of flexure of the detecting beams varies according to rigidity of the car floor or size of it. So that it is difficult to determine the gap from a calculated value of deformation of the rubber insulators before the installation of the car, hence it is necessary to adjust the gap by loading a weight at the site after the installation of the car.
In an alternative system, two load detecting switches are employed, one is provided at the underside of the car floor close to one rubber insulator, and the other is close to the other insulator on the diagonal line of the car floor. A problem associated with this system arises from a bias load on the car floor. That is, when the passengers stand on one side of the car floor, there could occur a phenomenon that one rubber insulator subsides deeply and the other makes no subsidence depending on the position where the load is placed. In this case, if two switches are connected to operate in parallel, they might be operated by a load smaller than the rated load. Also, if they are connected to operate in series, the bias load detecting performance will be unsatisfactory as it may occur that the switches will not operate unless the load applied on the floor is far above the rated load.